Battery pack, vehicle and control method for alleviating thermal runaway spreading of battery pack

ABSTRACT

The application discloses a battery pack, vehicle and control method for alleviating thermal runaway spreading of a battery pack. The battery pack includes a plurality of secondary batteries and a spray pipeline. A housing of the secondary battery includes a weakened portion, so that a heat flow resulting from thermal runaway of the secondary battery is able to break through the weakened portion to be discharged. The spray pipeline is corresponding to weakened portions of the secondary batteries and is arranged at a spacing B from the weakened portions of the secondary batteries. At least a portion of the spray pipeline corresponding to the weakened portions is a breakthrough region which is able to form an opening under an action of the heat flow. The spray medium in the spray pipeline is sprayed to a secondary battery in thermal runaway via the opening.

CROSS REFERENCE TO RELATED APPLICATION

The application is a continuation of International Application No. PCT/CN2020/107815 filed on Aug. 7, 2020, which claims the priority benefits of Chinese Patent Application No. 201910914674.5 filed on Sep. 26, 2019, both of which are incorporated herein by reference in their entireties.

FIELD

The application relates to the technical field of energy storing device, and in particular to a battery pack, a vehicle and a control method for alleviating thermal runaway spreading of battery pack.

BACKGROUND

New energy electric vehicles are becoming more and more popular as the problem of environmental protection receives increasing attention. The endurance mileage of an electric automobile is relevant to the energy density of a battery pack. In order to obtain high energy, the current battery packs employ relatively large number of secondary batteries for combination of series-parallel connection. As the energy density of the battery pack becomes higher and higher, the problem of thermal safety becomes more and more serious. The safety of the battery pack has a direct impact on the safety for the electric automobile as well as the passengers, and thus the safety problem for the battery pack has become a barrier to the further promotion of electric automobiles. It has become an urgent technical problem how to effectively solve the safety problem for the battery pack.

SUMMARY

A first aspect of the application provides a battery pack including:

a plurality of secondary batteries, a housing of each of which includes a weakened portion, so that a heat flow resulting from thermal runaway of the secondary battery is able to break through the weakened portion to be discharged;

a spray pipeline which is corresponding to weakened portions of the secondary batteries and is arranged at a spacing B from the weakened portions of the secondary batteries, at least a portion of the spray pipeline corresponding to the weakened portions being a breakthrough region which is able to form an opening under an action of the heat flow, a spray medium in the spray pipeline being sprayed to an abnormal secondary battery in thermal runaway via the opening;

a capacity A of the secondary battery by Ah and a spacing B between the weakened portion and the spray pipeline by mm satisfy:

10

3×[(A+25)/B]^(0.5)

35.

Optionally, 15

3×[(A+25)/B]^(0.5)

28.

Optionally, 17.5

3×[(A+25)/B]^(0.5)

28.

In any of the above embodiments in the first aspect of the application, the spacing B between the weakened portion and the spray pipeline is 0.5 mm-25 mm, optionally within 1 mm-15 mm, further optionally within 2 mm-10 mm.

In any of the above embodiments in the first aspect of the application, a width C of the spray pipeline and the spacing B between the weakened portion and the spray pipeline may satisfy:

1

(0.6C/B)^(0.5)

5.5; Optionally, 1.5

(0.6C/B)^(0.5)

2.5;

in which units for C and B are both mm.

In any of the above embodiments in the first aspect of the application, the breakthrough region of the spray pipeline may face directly towards the weakened portions of the secondary batteries.

In any of the above embodiments in the first aspect of the application, the battery pack may further includes a storage case; the spray pipeline is connected to the storage case, and at least a portion of the spray pipeline is located above the secondary batteries; or the spray pipeline includes a plurality of pipeline units arranged in parallel, each of the plurality of pipeline units being arranged corresponding to at least one of the secondary batteries and each of the plurality of pipeline units being connected to the storage case.

In any of the above embodiments in the first aspect of the application, the storage case may include:

a case body including a cavity;

a separator located in the cavity of the case body, the separator separating the case body into a liquid storage part and a gas storage part, where the liquid storage part is in communication with the spray pipeline, the gas storage part including an inlet for inflow of a compressed gas, the separator being able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the compressed gas in the gas storage part.

Optionally, the separator is a separator plate or an elastic separator film. When the separator is a separator plate, the separator plate is slidably connected to an inner wall of the case body.

In any of the above embodiments in the first aspect of the application, the storage case may include:

a case body including a cavity;

a drive device disposed in the cavity of the case body, the drive device including an elastic member and a drive member, the elastic member being connected to the drive member, the drive member and a wall of the storage case enclosing and forming a liquid storage part in communication with the spray pipeline;

the drive member is able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the elastic force of the elastic member.

In any of the above embodiments in the first aspect of the application, there may be a height difference between the storage case and the breakthrough region of the spray pipeline. Optionally, the storage case is arranged higher than the breakthrough region of the spray pipeline.

In any of the above embodiments in the first aspect of the application, the breakthrough region includes a hot melt part to melt under a thermal action of the heat flow sprayed by the weakened portion of the secondary battery in order to form the opening; or the breakthrough region includes a stress concentration part to break up under an impact action of the heat flow sprayed by the weakened portion of the secondary battery in order to form the opening.

In any of the above embodiments in the first aspect of the application, a melting point of the hot melt part may be 200° C.-500° C., optionally 300° C.-500° C.

In any of the above embodiments in the first aspect of the application, the weakened portion may be a vent disposed on the housing; or the weakened portion may be formed through providing a notch or a thickness-reduced region on the housing.

In any of the above embodiments in the first aspect of the application, a latent heat D of the spray medium may be above 100 kJ/kg, optionally 200 kJ/kg-5000 kJ/kg, further optionally 200 kJ/kg-2000 kJ/kg.

In any of the above embodiments in the first aspect of the application, the spray medium may be one or more selected from: fire-control gas, fire-control liquid, fire-control colloid and fire-control powder. Optionally, the spray medium is one or more selected from: water, ethylene glycol, liquid nitrogen, liquid argon, liquid carbon dioxide, liquid heptafluoropropane and fluorinated ketone.

A second aspect of the application provides a vehicle including the battery pack according to the first aspect of the application.

A third aspect of the application provides a control method for alleviating thermal runaway spreading of a battery pack, in which the battery pack is the battery pack according to the first aspect of the application, the method including:

the heat flow resulting from thermal runaway of the secondary battery breaking through the weakened portion and acting on the spray pipeline, so that the breakthrough region forms the opening under the action of the heat flow;

the spray medium being sprayed to the secondary battery in thermal runaway via the opening to alleviate the thermal runaway spreading of the battery pack.

In any of the above embodiments in the third aspect of the application, a spray pressure P of the spray pipeline and the capacity A of the secondary battery may satisfy

${\frac{P}{\left( {{{0.0}6A} + 5} \right)} \geqslant 1};$

in which a unit for P is kPa, and a unit for A is Ah.

In any of the above embodiments in the third aspect of the application, a spray pressure P of the spray pipeline is above 10 kPa, optionally within 12 kPa-150 kPa.

In the battery pack, the vehicle and the control method for alleviating thermal runaway spreading of the battery pack as provided by the application, the heat flow resulting from thermal runaway of the secondary battery can break through the weakened portion of its housing to be discharged and act on the breakthrough region of the spray pipeline. The breakthrough region is able to form an opening under an action of the heat flow, so that the spray medium in the spray pipeline is sprayed to the secondary battery in thermal runaway via the opening. Also, the capacity A of the secondary battery and the spacing B between the weakened portion and the spray pipeline satisfy a specific relationship. Thus, the spray medium can fully act on the secondary battery in thermal runaway, effectively reduce the high temperature resulting from thermal runaway of the secondary battery and prevent the heat from spreading to other secondary batteries, so that the thermal runaway of the abnormal secondary battery is controlled effectively while the thermal runaway spreading in the battery pack is alleviated effectively. Therefore, the battery pack of the application has a relatively high safety performance.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the technical solutions in embodiments of the application more clearly, the drawings to be used in the embodiments of the application will be briefly described below. Obviously, the drawings described below are merely some embodiments of the application, and it is also possible for a person of ordinary skill in the art to obtain further drawings from these drawings without creative work.

FIG. 1 is a schematic structural view of a battery pack according to an embodiment of the application with the external packing and other accessories of the battery pack being omitted.

FIG. 2 is a schematic partial structural view of FIG. 1.

FIG. 3 is a schematic structural view of another battery pack according to an embodiment of the application with the external packing and other accessories of the battery pack omitted

FIG. 4 is a schematic structural view of another battery pack according to an embodiment of the application with the external packing and other accessories of the battery pack omitted

FIG. 5 is a schematic structural view of a storage case according to an embodiment of the application.

FIG. 6 is a schematic structural view of another storage case according to an embodiment of the application.

LIST OF REFERENCES

-   10 secondary battery; 11 weakened portion; -   20 spray pipeline; 21 breakthrough region; 22 pipeline unit; -   30 storage case; 31 case body; 31 a liquid storage part; 31 b gas     storage part; 32 separator; 33 drive device; 33 a elastic member; 33     b drive member; 33 c limit member; c1 first limit arm; c2 second     limit arm; -   40 sparger; 41 connection port.

It should be noted that the drawings are not plotted in actual proportion.

DETAILED DESCRIPTION

For more clearly understanding of the inventive purpose, technical solution and beneficial technical effect of the application, the application will be described in further details in combination with the embodiments. It is to be appreciated that the embodiments described herein are only intended to explain the application rather than to limit it.

For the sake of simplicity, only some numerical ranges are explicitly disclosed herein. However, any low limit may be combined with any high limit to form an unspecified range, and any lower limit may be combine with other lower limits to form an unspecified range, and also, any upper limit may be combined with any other upper limits to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is to be contained within the range. Thus, each point or individual value may be combined as its own lower or upper limit with any other point or individual value or with other lower or upper limits to form an unspecified range.

In the description herein, it is noted that, except as otherwise noted, the term “a number of” means one or more; “a plurality of” means two or more; “above”, “below” means including the number; the orientation or position relationship indicated by the terms “upper”, “lower”, “left”, “right”, “inner”, “outer” and the like is the orientation or position relationship as shown in the drawings, which is only for the purpose of description and brief description, rather than indicating or implying that the noted device or element is necessarily of the specific orientation or structured or operated in the specific orientation, thus, can not be regarded as limiting of the application.

In the description of the application, it is also noted that, except as otherwise stipulated or limited explicitly, the terms “mount”, “link”, “connect” shall be interpreted expansively, for example, it may be fixed connection, removable connection or integral connection; may be direct connection or indirect connection via an intermediate medium. For a person of ordinary skill in the art, the specific meaning of the above terms in the application can be interpreted depending on the specific situation.

In the description herein, the term “or” is inclusive unless otherwise indicated. In other word, that phrase “A or B” means “A, B, or both A and B”. More specifically, the condition “A or B” is satisfied by any of the following conditions: A is true (or present) and B is false (or not present); A is false (or not present) while B is True (or is present); or both A and B are true (or are present).

The above summary of the application is not intended to describe each and every embodiment or implementation disclosed by the application. The following description exemplify the exemplary embodiments in more detail. In various places throughout the application, guidance is provided by a series of embodiments which may be used in various combinations. In various embodiments, the enumeration is merely a representative group and should not be construed as exhaustive.

In order to solve the thermal safety problem of the battery pack and improve the safety performance of the battery pack, an embodiment of the application provides a battery pack. Referring to FIGS. 1 and 2, the battery pack in an embodiment of the application includes secondary batteries 10 and a spray pipeline 20.

A housing of the secondary battery 10 includes a weakened portion 11, so that a heat flow resulting from thermal runaway of the secondary battery 10 is able to break through the weakened portion 11 to be discharged.

The spray pipeline 20 is corresponding to the weakened portions 11 and is arranged at a spacing from the weakened portions 11. At least a portion of the spray pipeline 20 corresponding to the weakened portions 11 is a breakthrough region 21 which is able to form an opening under an action of the heat flow. The spray medium in the spray pipeline 20 is sprayed to an abnormal secondary battery 10 in thermal runaway via the opening.

In the battery pack, a capacity of the secondary battery 10 by Ah is A, a spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 is B, and A and B satisfy:

10

3×[(A+25)/B]^(0.5)

35.

For the sake of convenience, a spacing parameter K=3×[(A+25)/B]^(0.5) between the weakened portion of the secondary battery 10 and the spray pipeline 20 is defined. That is, 10≤K≤35. Only numerical calculation is involved in the computational equation for the spacing parameter K. For example, the capacity A of the secondary battery 10 is 205 Ah, and the spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 is 6 mm, and then:

K=3×[(A+25)/B]^(0.5)=3×[(205+25)/6]^(0.5)=18.6.

In the battery pack of the embodiment of the application, the heat flow resulting from thermal runaway of the secondary battery 10 can break through the weakened portion 11 of its housing to be discharged and act on the breakthrough region 21 of the spray pipeline 20. The breakthrough region 21 can form an opening under an action of the heat flow, so that the spray medium in the spray pipeline 20 is sprayed to the abnormal secondary battery 10 in thermal runaway via the opening. In addition, the study by the inventor has found that the capacity A of the secondary battery 10 and the distance B between the weakened portion 11 and the spray pipeline 20 satisfy a specific relationship, so that the spray medium can more sufficiently act on the secondary battery in thermal runaway. This can effectively reduce the high temperature resulting from thermal runaway of the secondary battery 10 and prevent the heat from spreading to other secondary batteries 10, so that the thermal runaway of the abnormal secondary battery 10 is controlled effectively while the thermal runaway spreading in the battery pack is alleviated effectively. Therefore, the battery pack in the embodiment of the application has a relatively high safety performance.

In addition, in the battery pack in the embodiment of the application, it is the heat flow discharged upon thermal runaway of the secondary battery 10 that triggers the spray pipeline 20 to spray. The battery pack responds quickly and accurately to thermal runaway of the secondary battery 10. In addition, the thermal runaway monitoring device and the spray control device provided in the battery pack may be dispensed with, so that the structure thereof is simple, and in particular, both the weight and the volume of the battery pack are relatively small, which is advantageous for it to have a high weight energy density and volumetric energy density.

The type of the secondary battery 10 is not particularly limited in the application, in which materials known in the art may be used for each of the positive and negative electrode active materials, the electrolyte, and the like. The secondary battery 10 generally encapsulates the electrode assembly and the electrolyte in the housing. In the housing of the secondary battery 10, the weakened portion 11 may be a vent disposed on the housing. Or the weakened portion 11 may be formed through providing a notch or a thickness-reduced region on the housing of the secondary battery 10.

The various materials in the secondary battery 10 undergo a reaction such as thermal decomposition or even combustion upon thermal runaway, and the internal temperature and pressure are rapidly increased. When the pressure in the secondary battery 10 reaches at a certain limit, the high-temperature and high-pressure mixed fluid may break through the weakened portion 11 of the housing to reduce the pressure inside the housing for the function of explosion-proof. That is, the heat flow is a high-temperature, high-pressure mixed fluid which is sprayed via the weakened portion 11 upon thermal runaway of the secondary battery 10. The mixed fluid includes a gas and a liquid at high temperature and high pressure, in which the liquid is mainly an electrolyte.

The breakthrough region 21 of the spray pipeline 20 is arranged corresponding to the weakened portion 11 of the secondary battery 10, so that the heat flow sprayed by the secondary battery in thermal runaway can act directly on the breakthrough region 21 to form an opening. In addition, this allows the spray pipeline 20 to spray the spray medium corresponding to the source of the heat flow, so that spreading of the heat flow may be reduced more effectively, thereby improving the control efficiency of thermal runaway as well as its spreading. In particular, the breakthrough region 21 arranged corresponding to the weakened portion 11 also enables the spray medium to flow into the interior of the housing of the secondary battery 10. It can suppress a reaction such as further thermal decomposition, combustion and the like of the material inside the housing, and control the continued generation of the heat flow, thereby further improving the control efficiency of thermal runaway and its spreading.

In some embodiments, the breakthrough region 21 of the spray pipeline 20 faces directly towards the weakened portion 11 of the secondary battery 10. For example, the housing top of the secondary battery 10 is provided with a vent, with the breakthrough region 21 of the spray pipeline 20 located directly above the vent and spaced apart from the latter.

There may be a plurality of ways to provide a breakthrough region 21 in the spray pipeline 20. As an example, at least a portion of the spray pipeline 20 corresponding to (or facing directly towards) the weakened portion 11 includes a hot melt part. The melting point of the hot melt part is lower than that of other regions of the spray pipeline 20, and the hot melt part can be melted to form the opening at the high temperature of the heat flow sprayed by the secondary battery 10, thereby effecting spraying. For example, the temperature of the heat flow sprayed by the secondary battery 10 in thermal runaway may be above 500° C., such as 600° C. The melting point of the hot melt part is less than the temperature of the heat flow, so that it can be melted under the effect of the high temperature of the heat flow. The melting point of the hot melt part may be 200° C.-500° C., for example, 300° C.-500° C. The melting point of other regions of the spray pipeline 20 is greater than the temperature of the heat flow, so that it provides a flow channel for the spray medium to flow to the secondary battery 10 in thermal runaway for localized spray.

As another example, at least a portion of the spray pipeline 20 corresponding to (or facing directly towards) the weakened portion 11 includes a stress concentration part. The heat flow pressure sprayed by the weakened portion 11 of the secondary battery 10 is relatively high, and under the high-pressure impact of the heat flow, the stress concentration part is broken up due to low strength and stress concentration, thereby forming an opening and realizing spraying. Other regions of the spray pipeline 20 have sufficient strength not to be damaged.

It can be seen that, in the normal work state of the battery pack, the structure of the spray pipeline 20 is complete, and the spray medium is stored in the spray pipeline 20. During the charge and discharge cycle, a complex chemical reaction may occur inside the secondary battery 10, and it generally has a certain internal resistance, so that the secondary battery 10 may generate heat during normal operation. Now the spray medium stored in the spray pipeline 20 can also serve to cool down the secondary battery 10, which is advantageous for improving the cycle life of the secondary battery 10. When the secondary battery 10 sprays a heat flow upon thermal runaway, the heat flow causes the spray pipeline 20 to form an opening. The spray medium is sprayed to the secondary battery 10 in thermal runaway via the opening, thereby effectively controlling the thermal runaway and its spreading.

In some embodiments, the spacing parameter K between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 may be ≤35, ≤32, ≤30, ≤28, ≤25. Also, the spacing parameter K may be ≥10, ≥12, ≥15, ≥18, ≥20. In this way, the phenomenon that the spray medium sprayed via the openings is self-diffused or is scattered by the high-temperature and high-pressure heat flow is significantly reduced, so that more spray medium can be sprayed to the secondary battery 10 in thermal runaway, and more spray medium may enter the interior of the housing of the secondary battery 10 via the breakthrough of the weakened portion 11. Most of the heat generated by the secondary battery 10 in thermal runaway is absorbed at fixed points, whereby the temperature of the secondary battery 10 in thermal runaway can be effectively lowered, and the heat is prevented from being diffused to other secondary batteries 10. Also, the spray medium into the housing of the secondary battery can suppress a reaction such as further thermal decomposition, combustion and the like of the material inside the housing, and control the continued generation of the heat flow. Thereby the battery pack may have a better control effect for the thermal runaway of the secondary battery 10 as well as the spreading thereof. Optionally, 15≤K≤28. Optionally, 17.1≤K≤28. Optionally, 17.5≤K≤28.

In some embodiments, the spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 may be 0.5 mm-25 mm. For example, B may be above 0.5 mm, above 1 mm, above 2 mm, or above 5 mm. And B may be below 25 mm, below 20 mm, below 15 mm, or below 10 mm. A appropriate spacing between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 is favorable for the battery pack to have a better control effect of thermal runaway and thermal runaway spreading, thereby improving the safety performance of the battery pack.

Optionally, the spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 may be 1 mm-15 mm, for example, 2 mm-10 mm.

The areas of the weakened portions 11 are different for the secondary batteries 10 of different capacities. The higher the capacity, the larger the area of the weakened portion 11 is required for the secondary battery 10. In some embodiments, the width C of the spray pipeline 20 and the spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20 satisfy:

1

(0.6C/B)^(0.5)

5.5

in which units for C and B are both mm.

In this context, the characteristic parameter T=(0.6C/B)^(0.5) of the spray pipeline 20 are defined. The characteristic parameter T reflects the specific relationship between the width C of the spray pipeline 20 and the spacing B between the weakened portion 11 of the secondary battery 10 and the spray pipeline 20. The study by the inventor has found that, when the characteristic parameter T is within the above range, the battery pack can have a high control effect on thermal runaway and thermal runaway spreading while ensuring that the spray pipeline 20 has a high mechanical performance.

If the characteristic parameter T≤5.5, optionally ≤4, further optionally ≤2.5, a large amount of high-temperature and high-pressure heat flow generated upon thermal runaway of the secondary battery 10 can be discharged in time to prevent the secondary battery 10 from bursting; meanwhile, it can also effectively prevent the high-temperature and high-pressure heat flow from blowing the spray medium away, so that the thermal runaway control function of the spray medium can be fully exerted. Further, the spray pipeline 20 can have a high rigidity if the characteristic parameter T≤5.5, so that it can be effectively prevented from being broken by the high-pressure heat flow, and the spray medium is ensured to be sprayed and positioned on the secondary battery 10 in thermal runaway. In addition, if the characteristic parameter T≤5.5, the spray pipeline 20 can also have a smaller volume and weight.

If the characteristic parameter T≥1, optionally ≥1.5, and further optionally ≥2, the spray pipeline 20 can be fully guaranteed to form an opening under an action of the heat flow, and more spray medium can enter the housing of the secondary battery 10. Therefore, the battery pack has a higher control effect on thermal runaway and thermal runaway spreading.

Optionally, the characteristic parameter T satisfies: 1.5≤T≤2.5.

The spray medium may be a material known in the art which can be used to control thermal runaway of the battery. For example, the spray medium may be selected from: fire-control gas, fire-control liquid, fire-control colloid and fire-control powder and the like. As a specific example, the spray medium may be one or more selected from: water, ethylene glycol, liquid nitrogen, liquid argon, liquid carbon dioxide, liquid heptafluoropropane and fluorinated ketone.

In some embodiments, a latent heat of the spray medium may be above 100 kJ/kg, above 200 kJ/Kg, above 500 kJ/kg, above 1000 kJ/kg, above 1500 kJ/kg, or above 2000 kJ/kg. The latent heat of the spray medium is large, which can absorb more heat, so that the temperature of the secondary battery 10 in thermal runaway and the heat flow released therefrom can be rapidly reduced, thereby improving the effect of alleviating thermal runaway of the battery pack. In addition, when the amount of heat released by thermal runaway of the secondary battery 10 is constant, the greater the latent heat of the spray medium, the less the amount of spray medium is required. It is advantageous for reducing the weight of the entire system.

In some embodiments, the latent heat of the spray medium may be below 5000 kJ/kg, below 4500 kJ/kg, below 4000 kJ/kg, below 3500 kJ/kg, or below 3000 kJ/kg. In this way, the weight of the spray medium satisfying the requirements is appropriate, so that the volume of the spray medium sprayed to alleviate thermal runaway spreading is appropriate, which can sufficiently acts on the secondary battery 10 in thermal runaway and the heat flow released therefrom, thereby effectively controlling thermal runaway of the secondary battery 10 and its spreading.

There may be a plurality of ways to enable spraying the spray medium to the abnormal secondary battery 10 in thermal runaway from the spray pipeline 20.

In some embodiments, referring to FIG. 3, the spray pipeline 20 may be a consecutive pipeline which is at least partly corresponding to all the secondary batteries 10 in the battery pack. In that pipeline, a spraying medium which can meet the requirement of reduce the thermal runaway spreading of the battery pack can be encapsulate. When one of the secondary batteries 10 in the battery pack is subjected to thermal runaway, the heat flow causes an opening to form in the breakthrough region 11 of the spray pipeline 20 corresponding to the secondary battery 10, and the spray medium in the pipeline is sprayed from the opening to the secondary battery 10, thereby effectively controlling thermal runaway and its spreading.

In other embodiments, referring to FIG. 4, the spray pipeline 20 may include a plurality of pipeline units 22, each of which is arranged corresponding to at least one of the battery cells in the battery pack and may encapsulate a spray medium meeting the consumption demand to alleviate thermal runaway spreading of the battery. Each battery cell may include more than one secondary battery 10.

For example, the battery pack may include a plurality of battery cells arranged in the width direction of the battery pack, each of which may include a plurality of secondary batteries 10 arranged in the length direction of the battery pack. Each battery cell may be provided with one pipeline unit 22 respectively.

When a certain secondary battery 10 in any battery cell is subjected to thermal runaway, the breakthrough region 11 of the pipeline unit 22 corresponding to the battery cell forms an opening under an action of the heat flow, so that the spray medium in the pipeline unit 22 is sprayed to the secondary battery 10 in thermal runaway, thereby effectively controlling thermal runaway of the secondary battery 10 and its spreading. Since a pipeline unit 22 with a spray medium is provided for each battery cell, when the secondary batteries in a plurality of different battery cells 10 are subjected to thermal runaway, spray mediums meeting the consumption demand can be sprayed to them independently and rapidly by the pipeline units 22 corresponding thereto for position-specific spray. The control efficiency for the thermal runaway as well as the spreading thereof inside the battery pack is further improved.

In some embodiments, the battery pack may further include a storage case 30.

If the spray pipeline 20 is a consecutive pipeline corresponding to all the secondary batteries 10 in the battery pack, the storage case 30 may be in communication with either end or both ends of the consecutive pipeline. Moreover, it may be the case that one storage case 30 is in communication with both ends of the consecutive pipeline respectively; or it may be the case that one of two storage cases 30 is in communication with an end of the consecutive pipeline and the other is in communication with the other end of the consecutive pipeline. Further, at least a portion of the spray pipeline 20 may be located above the secondary batteries 10.

If the spray pipeline 20 includes a plurality of pipeline units 22, the storage case 30 may be in communication with either end or both ends of each pipeline unit 22. For example, there may be a plurality of storage cases 30, each of which is independently in communication with either end or both ends of at least one pipeline unit 22. Alternatively, there may be one storage case 30, to which either end or both ends of each of the plurality of pipeline units 22 is/are connected. That is, the plurality of pipeline units 22 in the spray pipeline 20 are arranged in parallel.

Optionally, the battery pack may include a sparger 40. The sparger 40 includes a plurality of medium outlets (not shown in the drawings), via which the sparger 40 can be in communication with the plurality of pipeline units 22 respectively. As shown in FIG. 4, two spargers 40 are disposed at the opposite ends of the plurality of pipeline units 22 respectively with one sparger 40 in communication with one end of each pipeline unit 22 and the other sparger 40 in communication with the other end of each pipeline unit 22. A connection port 41 of the sparger 40 is in communication with the storage case 30. The sparger 40 is disposed between the storage case 30 and the spray pipeline 20 to split the spray medium in the storage case 30 into different pipeline units 22.

The storage case 30 in the battery pack may store the spray medium and is in communication with the spray pipeline 20. When the spray pipeline 20 sprays the spray medium to a secondary battery 10 in thermal runaway, the storage case 30 may provide the spray medium to the spray pipeline 20 to meet the consumption demand of the spray medium to alleviate thermal runaway spreading of the battery pack. That is, the spray medium meeting the consumption demand is stored in the spray pipeline 20 and the storage case 30. Moreover, it is possible to reduce the volume and weight of the spray pipeline 20 by storing a portion of the spray medium in the storage case 30, so that the volume and weight of the overall system can be reduced.

In some embodiments, the battery pack includes a storage case 30 and there may be a height difference between the storage case 30 and the opening. Specifically, the storage case 30 is located at a position higher than the opening of the spray pipeline 20. When the spray pipeline 20 is formed with an opening to spray, the spray medium in the storage case 30 due to the height difference applies a pressure to the spray medium in the spray pipeline 20. Thereby the spray medium may have a predetermined spray pressure. This enables the spray medium to overcome the flow resistance and the counter force of the high-pressure heat flow in the spray pipeline 20, which facilitates the spray of the spray medium via the opening. Specifically, the spray medium provided with a predetermined spray pressure can increase the spray amount of the spray medium and improve the utilization rate of the spray medium. More specifically, more spray medium can be introduced into the housing of the secondary battery 10 for better control of thermal runaway.

In some other embodiments, referring to FIG. 5, the storage case 30 includes a case body 31 including a cavity. A separator 32 is also provided in the case body and separates the case body 31 into a liquid storage part 31 a and a gas storage part 31 b. The liquid storage part 31 a is in communication with the spray pipeline 20. The gas storage part 31 b includes an inlet for inflow of a compressed gas to fill the gas storage part 31 b with gases. The separator 32 is able to drive the spray medium in the liquid storage part 31 a into the spray pipeline 20 under an action of the compressed gas in the gas storage part 31 b.

In the normal operation state of the battery pack, the spray medium is stored in the liquid storage part 31 a and the spray pipeline 20. Now the acting force of the spray medium in the liquid storage part 31 a on the separator 32 is balanced with the acting force of the compressed gas in the gas storage part 31 b on the separator 32. When a secondary battery 10 is subjected to thermal runaway, an opening forms in the spray pipeline 20 under the action of the heat flow, and the spray medium is sprayed to the secondary battery 10 in thermal runaway via the opening. Now the acting force of the spray medium in the liquid storage part 31 a on the separator 32 reduces, and the compressed gas in the gas storage part 31 b applies a drive force to the spray medium on the opposite side via the separator 32, so that the spray medium has a predetermined spray pressure. If necessary, gases may be added to the gas storage part 31 b via the inlet of the gas storage part 31 b to ensure that the compressed gas in the gas storage part 31 b has a sufficient pressure, thereby satisfying the requirement for the spray pipeline 20 to spray the spray medium with the weight and the spray pressure.

Optionally, the separator 32 may be a elastic separator film. When the spray pipeline 20 sprays, the acting force of the spray medium in the liquid storage part 31 a on the elastic separator film reduces, so that the elastic separator film is expanded under the action of the compressed gas in the gas storage part 31 b in order to cause the compressed gas to apply a pressure to the spray medium. As an example, the elastic separator film may be an involucra, such as an EPDM (Ethylene Propylene Diene Monomer) involucra.

Optionally, the separator 32 may also be a separator plate slidably connected to an inner wall of the case body 31. Thereby when the spray pipeline 20 sprays, the acting force of the spray medium in the liquid storage part 31 a on the separator plate reduces, so that the separator plate can move in the direction facing towards a fluid outlet of the liquid storage part 31 a under the action of the compressed gas in the gas storage part 31 b. As such, the compressed gas can apply a pressure to the spray medium via the separator plate.

Further, a sliding seal may also be provided between the outer peripheral wall of the separator plate and the inner wall of case body 31. By providing the sliding seal, it is possible to move the separator plate relative to the inner wall of the case body 31 while maintaining a good sealing effect and reducing the risk of the spray medium and/or the compressed gas flowing through between the outer peripheral wall of the separator plate and the inner wall of the case 31, so that the sensitivity of the motion of the separator plate is improved. For example, the sliding seal may be a packing seal or the like.

In some other embodiments, referring to FIG. 6, the storage case 30 includes a case body 31 including a cavity, with a drive device 33 provided in the case body. The drive device 33 includes an elastic member 33 a and a drive member 33 b. The elastic member 33 a is connected to the drive member 33 b, and the drive member 33 b and a wall of the case body 31 enclose and form a liquid storage part 31 a in communication with the spray pipeline 20. The drive member 33 a is able to drive the spray medium in the liquid storage part 31 a into the spray pipeline 20 under an action of the elastic force of the elastic member 33 a.

In the normal operation state of the battery pack, the spray medium is stored in the liquid storage part 31 a and the spray pipeline 20. Now the acting force of the spray medium in the liquid storage part 31 a on the drive member 33 b is balanced with the pressure of the elastic member 33 a on the drive member 33 b. When a secondary battery 10 is subjected to thermal runaway, an opening forms in the spray pipeline 20 under the action of the heat flow, and the spray medium is sprayed to the secondary battery 10 in thermal runaway via the opening. Now the acting force of the spray medium in the liquid storage part 31 a on the drive member 33 b reduces, and the elastic member 33 a applies a drive force to the spray medium on the opposite side via the drive member 33 b, so that the spray pipeline has a predetermined spray pressure.

An elastic member 33 a with an appropriate elastic force may be selected according to actual needs to ensure that it can provide a sufficient pressure to the spray medium to meet the weight and spray pressure requirements of the spray medium sprayed by the spray pipeline 20. For example, the elastic member 33 a may be selected from a spring, an elastic rubber, or the like.

The drive member 33 b may be a drive plate. The drive plate is slidably connected to an inner wall of the case body 31. Further, a sliding seal may also be provided between the outer peripheral wall of the drive plate and the inner wall of the case body 31. The function and type of the sliding seal may be those as previously described.

As an example, one end of the elastic member 33 a is connected to the inner wall of the case body 31, which may be an interference connection or a fixed connection. The other end of the elastic member 33 a is connected to the drive member 33 b. When the spray pipeline 20 is not spraying, the spray medium in the liquid storage part 31 a compresses the elastic member 33 a via the drive member 33 b, and the drive system is in a balanced and stable state. When the spray pipeline 20 sprays, the acting force of the spray medium in the liquid storage part 31 a on the drive member 33 b reduces, and the elastic restoring force of the elastic member 33 a acts on the spray medium via the drive member 33 b, so that the spray medium has a predetermined spray pressure.

As another example, the drive member 33 b is connected with elastic members 33 a at both ends respectively. Two drive members 33 b and the inner wall of the case body 31 enclose and form two liquid storage parts 31 b respectively. The two liquid storage parts 31 b are each provided with a fluid outlet which may be connected to one port of the spray pipeline 20 respectively. For example, the two liquid storage parts 31 b are connected to both ends of the aforesaid consecutive pipeline respectively, or are connected to both ends of the aforesaid pipeline unit 22. That is, the spray medium can enter from both ends of the consecutive pipeline or the pipeline unit 22 and be sprayed via the opening. This makes it possible to increase the weight and the pressure of the spray medium and to improve the effect of controlling thermal runaway and its spreading.

Further, a limit member 33 c may be provided between the drive members 33 b at both ends of the elastic member 33 a. When the spray pipeline 20 does not spray the spray medium, the limit member 33 c can strengthen the balance stability of the drive system. When the spray pipeline 20 sprays the spray medium, the limit member 33 c releases the limit action under the action of the elastic force of the elastic member 33 a, so that the elastic member 33 a applies the drive force to the spray medium.

As an example, the limit member 33 c includes a first limit arm c1 connected to one of the two drive members 33 b, and a second limit arm c2 connected to the other of the two drive members 33 b. When the spray pipeline 20 does not spray, the first limit arm c1 and the second limit arm c2 are bonded to each other, whereby the limit member 33 c plays a role of limit to enhance the balance stability of the drive system. When the spray pipeline 20 sprays, under the action of the elastic force of the elastic member 33 a, the bonding between the first limit arm c1 and the second limit arm c2 is released, thereby releasing the limit action, so that the elastic member 33 a applies a drive force to the spray medium. The bonding between the first limit arm c1 and the second limit arm c2 can be achieved by glue, glue strips or the like.

There may be one or more limit members 33 c disposed on the outer peripheral side of the elastic member 33 a, such as two or three limit members 33 c uniformly distributed on the inner peripheral side of the elastic member 33 a.

An embodiment of the application further provides a vehicle. The vehicle includes any battery pack in the embodiments of the application.

It will be appreciated that the vehicle may be, but is not limited to, a hybrid vehicle, a pure electric vehicle, or the like. In some embodiments, the vehicle may include a power source to supply power to the vehicle, and the battery pack is configured to supply electric energy to the power source.

The vehicle of the embodiments of the application adopts the battery pack of the embodiments of the application, and thus may also have corresponding advantageous effects, where the vehicle has a higher safety performance. When there is a secondary battery subjected to thermal runaway in the battery pack, the thermal runaway spreading of the battery pack can be effectively alleviated, which greatly prolongs the escape time for a person in the vehicle, thereby ensuring the personnel safety to a greater extent.

An embodiment of the application further provides a control method for alleviating thermal runaway spreading of a battery pack, in which the battery pack is any battery pack according to the embodiments of the application. The control method for alleviating thermal runaway spreading of a battery pack in the embodiment of the application includes:

S10, the heat flow resulting from thermal runaway of the secondary battery breaking through the weakened portion and acting on the spray pipeline, so that the breakthrough region of the spray pipeline forms the opening under an action of the heat flow.

S20, the spray medium being sprayed to the abnormal secondary battery in thermal runaway via the opening to alleviate the thermal runaway spreading of the secondary battery.

In the control method for alleviating thermal runaway spreading of a battery pack in the embodiment of the application, the heat flow resulting from thermal runaway of the secondary battery can break through the weakened portion of its housing to be discharged and act on the breakthrough region of the spray pipeline. The breakthrough region is able to form an opening under an action of the heat flow, so that the spray medium in the spray pipeline is sprayed to an abnormal secondary battery in thermal runaway via the opening. Also, the study by the inventor has found that if the capacity A of the secondary battery and the spacing B between the weakened portion and the spray pipeline satisfy a specific relationship, the spray medium can act on the secondary battery in thermal runaway more fully. This can effectively reduce the high temperature resulting from thermal runaway of the secondary battery and prevent the heat from spreading to other secondary batteries, so that the thermal runaway of the abnormal secondary battery is controlled effectively while the thermal runaway spreading in the battery pack is alleviated effectively. Therefore, the battery pack in the embodiment of the application has a relatively high safety performance.

In addition, in the control method for alleviating thermal runaway spreading of a battery pack in the embodiment of the application, it is the heat flow discharged upon thermal runaway of the secondary battery that triggers the spray pipeline to spray. The method responses quickly and accurately to thermal runaway of the secondary battery. In addition, the thermal runaway monitoring device and the spray control device provided in the battery pack may be dispensed with by means of the method, so that the structure of the battery pack is simple, and in particular, both the weight and the volume of the battery pack are relatively small, which is advantageous for the battery pack to have a high weight energy density and volumetric energy density.

A large amount of high temperature fluid may be produced upon thermal runaway of the secondary battery, resulting in a sharp increase in pressure inside the housing of the secondary battery. The study by the inventor has found that the spray pressure P at which the opening of the spray pipeline sprays to the secondary battery in thermal runaway and the capacity A of the secondary battery satisfy a specific relationship, where the resistance force to convey the spray medium in the spray pipeline and the pressure of the high temperature fluid may be overcome, so that more timely and efficient spraying of the spray medium to the secondary battery in thermal runaway may be achieved. The control efficiency for the thermal runaway of the secondary battery as well as the spreading thereof inside the battery pack can thereby be further improved.

A spray pressure of P at which the opening of the spray pipeline sprays to the secondary battery in thermal runaway and the capacity A of the secondary battery satisfy:

$\frac{P}{\left( {{{0.0}6A} + 5} \right)} \geqslant 1$

in which P indicates the spray pressure of the spray pipeline by kPa, and A indicates the capacity of the secondary battery 10 by Ah. Also, only numerical calculation is involved in the equation. For example, the spray pressure P of the opening is 120 kPa, and the capacity A of the secondary battery 10 is 180 Ah, which satisfy:

${\frac{P}{\left( {{{0.0}6A} + 5} \right)} = {\frac{120}{\left( {{{0.0}6 \times 180} + 5} \right)} = {{{7.5}9} > 1}}}.$

In some embodiments, the spray pressure P of the spray pipeline may be above 10 kPa, above 12 kPa, above 20 kPa, above 30 kPa, or above 50 kPa. It is advantageous for more effective control of thermal runaway of the secondary battery 10 as well as the spreading thereof. The spray pressure P of the spray pipeline may be below 150 kPa, below 120 kPa, below 100 kPa, or below 80 kPa. It may prevent a damage such as a breakage of the secondary battery 10 due to an excessive spray pressure, in order to avoid the high temperature and high pressure fluid spreading around, which is advantageous for alleviating the thermal runaway spreading inside the battery pack.

There may be a plurality of ways to achieve the spray pressure of P at which the opening of the spray pipeline sprays to the secondary battery in thermal runaway.

For example, in some embodiments, the battery pack includes a storage case and there may be a height difference between the storage case and the opening. Optionally, the storage case 30 is arranged higher than the opening of the spray pipeline. When the spray pipeline is formed with an opening to spray, the spray medium in the storage case due to the height difference applies a pressure to the spray medium in the spray pipeline, so that the spray pressure in the spray pipeline reaches at P.

In some other embodiments, the storage case includes a case body including a cavity. A separator is provided in the case body and separates the case body into a liquid storage part and a gas storage part. The liquid storage part is in communication with the spray pipeline. The gas storage part includes an inlet for inflow of a compressed gas to fill the gas storage part with gases. The separator is able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the compressed gas in the gas storage part. When spraying, the compressed gas in the gas storage part applies a drive force to the spray medium on the opposite side via the separator, so that the spray pressure of the opening reaches at P. If necessary, gases may be added to the gas storage part via the inlet of the gas storage part to ensure that the compressed gas in the gas storage part 31 b has a sufficient pressure, thereby satisfying the requirement for the spray pipeline to spray the spray medium with the weight and the spray pressure.

In some other embodiments, the storage case includes a case body including a cavity, with a drive device provided in the case body. The drive device includes an elastic member and a drive member. The elastic member is connected to the drive member, and the drive member and a wall of the case body enclose and form a liquid storage part in communication with the spray pipeline. The drive member is able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the elastic force of the elastic member. When the spray pipeline sprays, the elastic restoring force of the elastic member acts on the spray medium via the drive member, so that the spray pressure of the spray pipeline reaches at P.

Other details described herein for the battery pack in the embodiments of the application can also be applied to the method of this application, which will not be repeated here.

EMBODIMENTS

The following examples, which describe the disclosure of the application in more detail, are provided for illustrative purposes only, as various modifications and variations will be apparent to a person skilled in the art within the scope of the disclosure. Unless indicated otherwise, all of the reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all the instruments used in the examples are commercially available.

Embodiment 1

The battery pack is shown in FIG. 1, and includes a plurality of lithium ion secondary batteries, a spray pipeline located above the plurality of secondary batteries and spaced apart therefrom, and a storage case connected to the spray pipeline. A housing of each secondary battery includes a weakened portion, so that a heat flow resulting from thermal runaway of the secondary battery is able to break through the weakened portion to be discharged. The portion of the spray pipeline facing directly towards the weakened portion of the lithium ion secondary battery is a breakthrough region which is able to form an opening under an action of the heat flow. The capacity A of the secondary battery by Ah and the spacing B between the weakened portion and the spray pipeline by mm satisfy 3× [(180+25)/1.6]^(0.5)=34.0. Also, the width C of the spray pipeline and the spacing B between the weakened portion and the spray pipeline satisfy (0.6×28/1.6)^(0.5)=3.24.

The structure of the storage case is as shown in FIG. 5, which includes a case body including a cavity and a separator plate located in the cavity of the case body, and the separator plate separates the case body into a liquid storage part and a gas storage part. The liquid storage part is in communication with the spray pipeline, and the liquid storage part and the spray pipeline are provided with a spray liquid which is water. The gas storage part includes a compressed gas therein. The separator plate is able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the compressed gas in the gas storage part.

One of the secondary batteries in the battery pack is caused to undergo thermal runaway, for example, by overcharging, needling, or heating the secondary battery. The heat flow resulting from thermal runaway of the secondary battery breaks through the weakened portion and acts on the spray pipeline. The breakthrough region forms the opening under the action of the heat flow. The spray medium is sprayed to the secondary battery in thermal runaway via the opening to control thermal runaway and its spreading of the secondary battery.

Ten battery packs are tested and the success rate of thermal runaway control is recorded.

Control success rate of thermal runaway=number of battery packs without thermal runaway/total number of tested battery packs×100%

Embodiments 2-19 and Comparative Examples 1-6

It is similar to embodiment 1 with the exception that the related parameters of the battery pack are adjusted. Please see Table 1 for details.

TABLE 1 Success Rate Spacing B between of Thermal Capacity of the Weakened Width of Runaway Secondary Portion and the Spray Spreading Battery A Spray Pipeline pipeline Control Number [Ah] [mm] [mm] K T [%] Embodiment 180 1.6 28 34.0 3.24 90 1 Embodiment 180 2.4 28 27.7 2.65 100 2 Embodiment 180 6 28 17.5 1.67 100 3 Embodiment 180 15 28 11.1 1.06 80 4 Embodiment 180 18.5 28 10 0.95 70 5 Embodiment 51 5 9 11.7 1.04 80 6 Embodiment 51 2 9 18.5 1.64 100 7 Embodiment 300 2.5 52 34.2 3.53 90 8 Embodiment 300 20 52 12.1 1.25 80 9 Embodiment 300 10 52 17.1 1.77 100 10 Embodiment 5 2 2 11.6 0.77 70 11 Embodiment 205 6 30 18.6 1.73 100 12 Embodiment 95 6 15 13.4 1.22 80 13 Embodiment 95 3 15 19 1.73 100 14 Embodiment 180 6 50 17.5 2.24 100 15 Embodiment 180 6 10 17.5 1.00 90 16 Embodiment 180 6 23 17.5 1.52 100 17 Embodiment 180 6 9 17.5 0.95 80 18 Embodiment 180 1.6 85 34.0 5.65 80 19 Comparative 180 1.2 28 39.2 3.74 20 Example 1 Comparative 180 20 28 9.6 0.92 0 Example 2 Comparative 51 0.5 9 37 3.29 10 Example 3 Comparative 51 20 9 5.8 0.52 0 Example 4 Comparative 300 2 52 38.2 3.95 20 Example 5 Comparative 300 30 52 9.9 1.02 0 Example 6

Note: in Table 1 K=3×[(A+25)/B]^(0.5); T=(0.6C/B)^(0.5.)

As can be seen from the results of table 1, a spray pipeline is provided in the battery pack of the application and includes a breakthrough region in the weakened portion corresponding to the housing of the secondary battery. The breakthrough region is able to form an opening under an action of the heat flow resulting from thermal runaway of the secondary battery, so that the spray medium in the spray pipeline is sprayed to the abnormal secondary battery in thermal runaway via the opening. Also, the capacity A of the secondary battery and the spacing B between the weakened portion and the spray pipeline satisfy a specific relationship. Thus, the spray medium can act on the secondary battery in thermal runaway more fully, effectively reduce the high temperature resulting from thermal runaway of a secondary battery and prevent the heat from spreading to other secondary batteries, so that the thermal runaway of the abnormal secondary battery is controlled effectively while the thermal runaway spreading in the battery pack is alleviated effectively. Therefore, the battery pack of the application has a relatively high safety performance.

The capacity A of the secondary battery and the spacing B between the weakened portion and the spray pipeline in the comparative example cannot satisfy the above specific equation When a secondary battery in the battery pack is subjected to thermal runaway, it is impossible to control thermal runaway of the secondary battery well, so that the thermal runaway spreads in the battery pack, which is a serious potential safety hazard.

The above description is only specific embodiments of the application, but the protection scope of the application is not limited thereto. Various equivalent modifications or substitutions are readily conceivable within the technical scope disclosed herein for any person skilled in the art, which are intended to be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to that of the claims. 

What is claimed is:
 1. A battery pack, comprising: a plurality of secondary batteries, a housing of each of which comprises a weakened portion, so that a heat flow resulting from thermal runaway of each of the plurality of secondary batteries is able to break through the weakened portion to be discharged; a spray pipeline which is corresponding to the weakened portion of each of the plurality of secondary batteries and is arranged at a spacing B from the weakened portion of one of the plurality of secondary batteries, at least a portion of the spray pipeline corresponding to the weakened portion being a breakthrough region which is able to form an opening under an action of the heat flow, a spray medium in the spray pipeline being sprayed to an abnormal secondary battery in thermal runaway via the opening; wherein a capacity A of one of the plurality of secondary batteries by Ah and a spacing B between the weakened portion and the spray pipeline by mm satisfy: 10

3×[(A+25)/B]^(0.5)


35. 2. The battery pack according to claim 1, wherein 15

3×[(A+25)/B]^(0.5)


28. 3. The battery pack according to claim 1, wherein the spacing B between the weakened portion and the spray pipeline is 0.5 mm-25 mm.
 4. The battery pack according to claim 1, wherein a width C of the spray pipeline and the spacing B between the weakened portion and the spray pipeline satisfy: 1

(0.6C/B)^(0.5)

5.5; in which units for C and B are both mm.
 5. The battery pack according to claim 1, wherein the breakthrough region of the spray pipeline faces directly towards the weakened portion.
 6. The battery pack according to claim 1, wherein the battery pack further comprises a storage case; the spray pipeline is connected to the storage case, and at least a portion of the spray pipeline is located above the plurality of secondary batteries; or the spray pipeline comprises a plurality of pipeline units arranged in parallel, each of the plurality of pipeline units being arranged corresponding to at least one of the plurality of secondary batteries and each of the plurality of pipeline units being connected to the storage case.
 7. The battery pack according to claim 6, wherein the storage case comprises: a case body comprising a cavity; a separator located in the cavity of the case body, the separator separating the case body into a liquid storage part and a gas storage part, wherein the liquid storage part is in communication with the spray pipeline, the gas storage part comprising an inlet for inflow of a compressed gas, the separator being able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the compressed gas in the gas storage part.
 8. The battery pack according to claim 7, wherein the separator is a separator plate or an elastic separator film, and when the separator is the separator plate, the separator plate is slidably connected to an inner wall of the case body.
 9. The battery pack according to claim 6, wherein the storage case comprises: a case body comprising a cavity; a drive device disposed in the cavity of the case body, the drive device comprising an elastic member and a drive member, the elastic member being connected to the drive member, the drive member and a wall of the storage case enclosing and forming a liquid storage part in communication with the spray pipeline; wherein the drive member is able to drive the spray medium in the liquid storage part into the spray pipeline under an action of the elastic force of the elastic member.
 10. The battery pack according to claim 6, wherein there is a height difference between the storage case and the breakthrough region of the spray pipeline.
 11. The battery pack according to claim 1, wherein the breakthrough region comprises a hot melt part to melt under a thermal action of the heat flow in order to form the opening.
 12. The battery pack according to claim 1, wherein the breakthrough region comprises a stress concentration part to break up under an impact action of the heat flow in order to form the opening.
 13. The battery pack according to claim 11, wherein a melting point of the hot melt part is 200° C.-500° C.
 14. The battery pack according to claim 1, wherein the weakened portion is a vent disposed on the housing.
 15. The battery pack according to claim 1, wherein the weakened portion is formed through providing a notch or a thickness-reduced region on the housing.
 16. The battery pack according to claim 1, wherein a latent heat D of the spray medium is above 100 kJ/kg.
 17. The battery pack according to claim 1, wherein the spray medium is one or more selected from: fire-control gas, fire-control liquid, fire-control colloid and fire-control powder.
 18. A vehicle, comprising the battery pack according to claim
 1. 19. A control method for alleviating thermal runaway spreading of a battery pack, wherein the battery pack is the battery pack according to claim 1, the control method comprising: the heat flow resulting from thermal runaway of one of the plurality of secondary batteries breaking through the weakened portion and acting on the spray pipeline, so that the breakthrough region forms the opening under the action of the heat flow; the spray medium being sprayed to the secondary battery in thermal runaway via the opening to alleviate the thermal runaway spreading of the battery pack.
 20. The control method according to claim 19, wherein a spray pressure P of the spray pipeline and the capacity A of one of the plurality of secondary batteries satisfy: ${\frac{P}{\left( {{{0.0}6A} + 5} \right)} \geqslant 1};$ in which a unit for P is kPa, and a unit for A is Ah. 